Sealed secondary battery assemblies of this type are previously known and are disclosed in Laid-Open Japanese Patent Publication No.7-85847. This prior art example has a construction as shown in FIG. 16. Specifically, electricity generating elements are accommodated in battery cases 36 formed in rectangular tubular shape having a bottom, the apertures of these battery cases 36 are sealed by covers 37 to constitute cells 32, a plurality of which are arranged in series, the battery cases 36 of these cells 32 being connected in tightly restrained condition by means of end plates 35 and restraining straps 34. Also, pillar-shaped positive electrode terminals 38 and negative electrode terminals 39 of the cells 32 penetrate through covers 37 and project above them, these terminals 38 and 39 being electrically connected by means of an electrical connection bar 40.
However, with a construction as in the prior art example wherein battery cases 36 are tied together and held in restrained fashion by means of end plates 35 and restraining straps 34, when the cells 32 expand as for example during charging, a condition as shown in FIG. 17 is produced, with stress being concentrated at the portions indicated by P.
This stress concentration gives rise to creep deformation and as a result the durability of battery cases 36 in regard to vibration or shock is severely impaired.
Also, in the case of a construction as in the prior art example in which the positive electrode and negative electrode terminals 38 and 39 project above cover 37 and are electrically connected by an electrical connection bar 40, the secondary battery is increased in height by the amount to which the positive electrode and negative electrode terminals 38 and 39 project above cover 37; this is contrary to demands for increased compactness. Also, there was the problem that sealing had to be carried out individually between positive electrode and negative electrode terminals 38, 39 and cover 37 and if sealing was insufficient internal liquid or gas could leak directly to the outside.
Also, with a construction as in the prior art example wherein the electrical connection between the individual cells is effected on the outside, the positive electrode and negative electrode terminals 38 and 39 must be given a sealing function, electrical connection function, and function of effecting connection between themselves and the electricity-generating elements within the batteries. The construction of the positive electrode and negative electrode terminals 38 and 39 therefore becomes complicated and costly, and, as a result, the total cost of the sealed secondary battery assembly becomes high.
In the light of the above demands for compactness and demands for ensuring sealing strength and lowering costs, the inventors of the present invention conceived, as a way of solving the problems of the prior art example, an internally connected construction wherein electrical connection between the terminals is made within the batteries. In this internally connected construction, as shown in FIG. 19, electrical connection between two cells 32, 32 is made using an electrical connecting rod 41 that passes through the connecting walls 45, 45 of adjacent battery cases 36. Then, at the location Q where electrical connecting rod 41 passes through, the three items: electrical connecting rod 41 and the two connecting walls 45, 45 are integrally coupled by a resin welding technique.
However, if the internally connected construction shown in FIG. 18 is adopted, when cells 32 expand during charging etc., the condition shown in FIG. 17 is produced, with stress being concentrated in the portions shown by Q in FIG. 18. Such stress concentration produces creep deformation and this gives rise to the problem that the durability of battery cases 36 and electrical connecting rods 41 in regard to vibration and impact is severely impaired.
An object of the present invention is to solve the above problems and to provide a sealed secondary battery assembly of excellent cooling construction.